Carbon nanotubes (CNTs) are substantially cylindrical hollow architectures made of graphene sheets where the length-to-diameter ratio generally exceeds about 1,000. They have unusual properties making them potentially useful in applications such as nanotechnology, electronics, optics and other fields of materials science. They exhibit extraordinary mechanical, thermal and electrical properties. Their diameter is of the order of a few nanometers, and up to several millimeters in length. There are single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs) and multi-walled carbon nanotubes (MWCNTs), depending on the number of cylindrical graphene sheets forming the architecture.
For use in many applications, especially in composite applications, CNTs need to be bonded to other structural materials, for example to epoxy resins in thermoset composites. For this, i.e. grafting of chemical functions at the surface, functionalization is necessary. With SWCNTs, covalent functionalization will break some of the carbon-carbon double bonds and effectively leave a hole in the nanotube structure, with consequent modification of mechanical and electrical properties. With DWNTs, only the outer wall is modified.